Question

我有一个应用程序，我在RecyclerView中有几个视图（不同类型的列表项）。从数据库中获取数据后，每个项目都会更新。在滚动我的RecyclerView中的项目时，我遇到了粘性滚动的问题。我确信这是由于数据库访问操作而发生的，我试图解决这个问题。我在StackOverflow上提到了几个答案，并通过官方的android帖子（Making ListView Scrolling Smooth）阅读。正如在android帖子中所建议的，我使用AsyncTask将所有数据库访问操作移动到后台线程，但仍然没有找到运气。以下是我在onBindViewHolder内写的代码，用于更新其中一项。

new AsyncTask<RecyclerView.ViewHolder, Void, TaskPhysicalActivity>(){
                private RecyclerView.ViewHolder v;
                PhysicalActivityItemHolder pAItemHolder;
                DBHelper mDbHelper;
                User mUser;
                @Override
                protected TaskPhysicalActivity doInBackground(RecyclerView.ViewHolder... params) {
                    pAItemHolder = (PhysicalActivityItemHolder)params[0];
                    Calendar cal = Calendar.getInstance();
                    Calendar today = Calendar.getInstance();
                    Calendar earlier = Calendar.getInstance();
                    earlier.add(Calendar.DATE, -6);
                    mDbHelper = DBHelper.getInstance(mContext);
                    mUser = User.getDefaultUser(mContext);
                    try {
                        List<PhysicalActivity> physicalActivities = mDbHelper.getPhysicalActivityInRange(mUser, cal, cal);
                        PhysicalActivityReport physicalActivityReport = new PhysicalActivityReport(earlier.getTime(), today.getTime());
                        physicalActivityReport.makeReport(mContext, mUser);
                        int userStepGoal = PhysicalActivity.getDailyStepsGoal(mContext);
                        return new TaskPhysicalActivity(userStepGoal, physicalActivityReport.getPhysicalActivityList(), physicalActivities,physicalActivityReport);
                    } catch (ParseException e) {
                        e.printStackTrace();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }

                    return null;
                }


                @Override
                protected void onPostExecute(TaskPhysicalActivity taskPhysicalActivity) {
                    int stepsCount = 0;
                    Calendar cal = Calendar.getInstance();
                    TaskPhysicalActivity taskPhysicalActivityObject = taskPhysicalActivity;
                    List<PhysicalActivity> physicalActivities = taskPhysicalActivityObject.getPhysicalActivities();
                    List<PhysicalActivity> activityList = taskPhysicalActivityObject.getActivityList();
                    PhysicalActivityReport physicalActivityReport = taskPhysicalActivityObject.getPhysicalActivityReport();

                    pAItemHolder.tvActivityEmptyText.setVisibility(View.GONE);

                    if (physicalActivities.size() > 0) {
                        for (int i = 0; i < physicalActivities.size(); i++) {
                            stepsCount = stepsCount
                                    + physicalActivities.get(i).getValue();
                        }

                        final int finalStepsCount = stepsCount > 0 ? stepsCount : 0;
                        pAItemHolder.tvActivityValue.setText(String.valueOf(finalStepsCount));
                        pAItemHolder.tvActivityValueText.setText(mContext.getResources().getString(R.string.steps_unit));
                        pAItemHolder.tvActivityEmptyText.setText("");
                        pAItemHolder.vActivityCardEmptyView.setVisibility(View.GONE);
                        pAItemHolder.vActivityCardView.setVisibility(View.VISIBLE);

                    } else {

                        pAItemHolder.tvActivityValue.setText("--");
                        pAItemHolder.tvActivityValueText.setText(mContext.getResources().getString(R.string.steps_unit));
                        pAItemHolder.tvActivityEmptyText.setText("");
                        pAItemHolder.vActivityCardEmptyView.setVisibility(View.VISIBLE);
                        pAItemHolder.vActivityCardView.setVisibility(View.GONE);

                    }

                    pAItemHolder.tvActivityGoal.setText(String.format(mContext.getResources().getString(R.string.activity_goal_display_string),
                            taskPhysicalActivityObject.getUserStepsGoal(), mContext.getResources().getString(R.string.steps_unit), mContext.getResources().getString(R.string.per_day)));
                    pAItemHolder.vActivityGraph.setActivityValues(activityList);

                    if (physicalActivityReport.getPhysicalActivityAverage() > 0) {
                        pAItemHolder.tvPercentInRange.setText("Average steps " + physicalActivityReport.getPhysicalActivityAverage());
                    }
                    if (activityList.size() == 0) {
                        pAItemHolder.vActivityCardEmptyView.setVisibility(View.VISIBLE);
                        pAItemHolder.vActivityCardView.setVisibility(View.GONE);
                    } else {
                        pAItemHolder.vActivityCardEmptyView.setVisibility(View.GONE);
                        pAItemHolder.vActivityCardView.setVisibility(View.VISIBLE);
                    }
                }
            }.execute(holder);

在上面的代码中，doInBackground内的以下四行执行数据库访问：

List<PhysicalActivity> physicalActivities = mDbHelper.getPhysicalActivityInRange(mUser, cal, cal);
PhysicalActivityReport physicalActivityReport = new PhysicalActivityReport(earlier.getTime(), today.getTime());
physicalActivityReport.makeReport(mContext, mUser);
int userStepGoal = PhysicalActivity.getDailyStepsGoal(mContext);

我使用这些操作的结果来更新onPostExecute方法中的用户界面我使用AsyncTask的方式有问题吗？我错过了什么吗？

Answer 1

问题是，您在onBindViewHolder内调用此代码。这意味着，为RecyclerView内的每个新显示的行执行此代码（并在滚动时对同一行执行多次!!）。

如何将此代码移至Activity或Fragment（无论持有该列表）？这样，代码将执行一次。然后将您在此处解析的数据包装到自定义POJO对象中：

public class POJO {
    String activityValue;
    String activityValueText;
    String activityEmptyText;
    boolean activityCardEmptyViewVisibility;
    boolean activityCardViewVisibility;
}

将此类作为传递给RecyclerView的对象。然后，在onBindViewHolder内使用getItem(position)，然后将数据从POJO传递到Holder。

执行Activity内的所有逻辑（或任何控制器，pressenter，用于业务逻辑的任何内容）。这就是它注定的目标。 Adapter仅用于显示结果，而不用于为应用程序创建业务逻辑。

Answer 2

感谢@Rafal和@ r-zagórski提出的宝贵建议。我尝试了保持数据准备并将其传递给onBindViewHolder的方法，但由于某种原因没有帮助。然后我将onBindViewHolder中的所有代码移动到onCreateViewHolder，并将一个对象传递给适配器构造函数，其中包含已计算并打包在此对象中的所有必需参数。列出以下步骤：

创建一个类（比如DataClass）来保存所有必需的值，并在更新期间稍后在recyclerView适配器中使用它们的getter。

由于数据库访问是内存密集型的，因此使用AsyncTask在doInBackground方法中执行所有数据库访问操作，并使其返回DataClass的对象。

 protected DataClass doInBackground(Params... params) {
 //perform database or other operations here
 // Let's say DataClass constructor takes in 3 parameters which are later used to update recycler view 
    return new DataClass(data1, data2, data3);
 }

现在更新onPostExecute完成执行后调用的doInBackground方法内的recyclerView。我确信这不是最佳实践，但每次我想更新时都必须重新初始化适配器，因为我需要将DataClass对象传递给它。
```
protected void onPostExecute(DataClass dataObject) {
 mRecyclerViewAdapter = new RecyclerViewAdapter(dataObject, .....);
 mRecylerView.setAdapter(mRecyclerViewAdapter);
 //Notify Data set or Item changed if required
}
```
不要忘记为recyclerViewAdapter编写自定义构造函数，以便将dataObject传递给它。

我这样解决了我的问题。滚动是平滑的，除了第一次创建片段。

RecyclerView无法顺畅滚动

2 个答案: